fix Callable narrowing hack incorrectly being used on TypeIs

packages/pyright-internal/src/analyzer/typeGuards.ts

@@ -1818,7 +1818,12 @@ function narrowTypeForInstance(
 
             if (
                 isClass(subtype) ||
-                (getFileInfo(errorNode).diagnosticRuleSet.strictGenericNarrowing && isFunction(subtype))
+                // when strictGenericNarrowing is enabled, we need to convert the Callable type to a Callable
+                // protocol to make sure it keeps the generics when narrowing, but this is only needed for
+                // isinstance checks because you can't specify generics to it
+                (!isTypeIsCheck &&
+                    getFileInfo(errorNode).diagnosticRuleSet.strictGenericNarrowing &&
+                    isFunction(subtype))
             ) {
                 if (isFunction(subtype)) {
                     subtype = synthesizeCallableProtocolFromFunctionType(evaluator, subtype, errorNode);

packages/pyright-internal/src/tests/samples/typeNarrowingUsingBounds.py

@@ -1,4 +1,4 @@
-from typing import Any, Never, assert_type, runtime_checkable, Protocol, Iterable, Iterator, MutableMapping, Reversible, Callable
+from typing import Any, Never, assert_type, runtime_checkable, Protocol, Iterable, Iterator, MutableMapping, Reversible, Callable, TypeIs
 from types import FunctionType
 
 class Covariant[T]:
@@ -134,4 +134,10 @@ def _(f: CallableProtocol[[], None]):
 
 def _(f: Callable[[int], str]):
     if isinstance(f, FunctionType):
-        assert_type(f, FunctionType)
+        assert_type(f, FunctionType)
+
+def takes_arg(value: object) -> TypeIs[Callable[[int], None]]: ...
+
+def _(value: Callable[[], None] | Callable[[int], None]):
+    if takes_arg(value):
+        assert_type(value, Callable[[int], None])

packages/pyright-internal/src/tests/samples/typeNarrowingUsingBoundsDisabled.py

@@ -1,4 +1,4 @@
-from typing import Any, assert_type, runtime_checkable, Protocol, Iterable, Iterator, MutableMapping, Reversible, Callable
+from typing import Any, assert_type, runtime_checkable, Protocol, Iterable, Iterator, MutableMapping, Reversible, Callable, TypeIs
 from types import FunctionType
 
 
@@ -132,4 +132,10 @@ def _(f: CallableProtocol[[], None]):
 
 def _(f: Callable[[int], str]):
     if isinstance(f, FunctionType):
-        assert_type(f, FunctionType)
+        assert_type(f, FunctionType)
+
+def takes_arg(value: object) -> TypeIs[Callable[[int], None]]: ...
+
+def _(value: Callable[[], None] | Callable[[int], None]):
+    if takes_arg(value):
+        assert_type(value, Callable[[int], None])